[FIX] mail: overflow in the attachment box
[FIX] mail: overflow in the attachment box

The chatter's attachment box has an horizontal overflow when adding at
least 1 attachment.

This is due to a negative margin applied on the attachment list/previews
not matching its container's padding (3px vs 5px).

This commit reuses the SCSS variable dedicated to this margin around the
attachment list/previews and apply it correctly to the chatter's
attachment box.

Task ID: 2194025

X-original-commit: 3a7eb3fe97541855ae893514f8b98cbfe6c1a7e4
ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo